The present invention relates to a method and apparatus for determining the cardiovascular condition of a patient, and more particularly to a method and apparatus for monitoring aortic valve abnormalities such as aortic regurgitation.
A. The Pathology of Aortic Regurgitation.
Heart valve abnormalities are a major component of cardiovascular disease. Aortic Regurgitation (AR), also known as Aortic Insufficiency (AI), is probably the most common valvular problem. Each year thousands of patients experience cardiovascular function problems as a result of aortic regurgitation. Eventually many of these cases lead to the need for surgical intervention such as aortic valve replacement. Therefore, the detection and evaluation of aortic regurgitation is extremely important in those subjects with suspected cardiovascular disease. The development of a simple, inexpensive technique by which to screen individuals for aortic regurgitation is extremely important in those subjects with suspected cardiovascular disease. The development of a simple, inexpensive technique and apparatus with which one can screen individuals for aortic regurgitation represents an advance in medical instrumentation.
Aortic regurgitation may be caused by a variety of diseases or acute trauma. In the case of disease, the process may act directly on the aortic valve leaflet or the wall of the aortic root. Approximately two-thirds of severe aortic regurgitation cases which result in aortic valve replacement are caused by leaflet abnormalities. As used in this application, the term xe2x80x9caortic valve abnormalitiesxe2x80x9d is broad enough to encompass all of the various conditions which result in aortic regurgitation.
Rheumatic fever is a common disease mechanism of many valve leaflet abnormalities. The fever causes the cusps to become infiltrated with fibrous tissues and retract, a process that prevents the cusps from closing during diastole. This usually results in AR in the left ventricle through the center of the valve. Diseases such as infective endocarditis may cause aortic regurgitation through a similar mechanism.
In contrast, diseases such as Syphilis, Ankylosing Spondylitis, Rheumatoid Arthritis, and Marfan Syndrome may produce aortic regurgitation by causing marked dilation of the ascending aorta. In each of these diseases, the aortic annulus may become greatly dilated, the aortic leaflets may separate, and AR may ensue. In addition, the dilation of the aortic root may have a secondary effect on the aortic valve, since it may cause tension and bowing of the cusps which may thicken, retract, and become too short to close the aortic orifice.
Acute trauma may produce aortic regurgitation as a result of mechanical damage. For example, a tear in the ascending aorta may cause loss of valve leaflet support and therefore lead to the initiation of regurgitation.
Regardless of the etiology, Aortic Regurgitation usually produces dilation and hypertrophy of the left ventricle as a result of the chronic regurgitant flow. It may also produce dilation of the mitral valve ring and the left atrium. These changes represent cardiovascular system adaptation as a result of chronic or gradually increasing aortic regurgitation. The systemic response permits the ventricle to perform as an effective high compliance pump. As a result, patients with severe chronic AR have the largest end-diastolic volumes of those with any form of heart disease.
High end-diastolic and stroke volumes assist in maintaining proper cardiovascular function. As the left ventricle dilates, ventricular function deteriorates due to the inability to efficiently move blood out of the heart. Rising end-diastolic volumes eventually cannot compensate for the regurgitant volume, and the ejection fraction and forward stoke volume decline. In order to restore forward stroke volume and ventricular function, aortic valve replacement usually must be performed.
Unfortunately, the cardiovascular system cannot adapt quickly to acute aortic regurgitation. As a result, the back flow of blood through the damaged valve will fill the ventricle. A ventricle of normal size cannot accommodate the combined large regurgitate volume and atrium inflow. Since total stroke volume cannot rise due to structural constraints, forward stroke volume will decline. In response, left ventricle diastolic pressure may rise quickly, and cardiac function may drop drastically. Cardiovascular complications may ensue quickly threatening the life of the patient.
B. Prior Art Methods for Detecting and Evaluating Aortic Regurgitation.
The state-of-the-art methods for detecting aortic regurgitation and either evaluating the severity of disease or quantifying the amount of regurgitate volume include echocardiography, invasive catheterization, and magnetic resonance imaging (MRI).
A variety of echocardiography techniques can be utilized to evaluate aortic regurgitation. Although M-mode or two-dimensional ultrasound may be quite useful to detect aortic regurgitation or structural changes, the addition of Doppler may be quite useful to measure the outflow velocity from the aortic valve. When combined with measurements of valve diameter, the flow can be calculated. Color flow Doppler represents a drastic improvement in echo imaging due to the ability to approximate the regurgitate volume. Additionally, continuous wave Doppler may also be a useful technique to evaluate the severity of the disease in which the deceleration slope of the ventricular pressure gradient is evaluated. This is accomplished using the Bernoulli equation which relates velocity changes to a pressure gradient.
Invasive techniques may also be used to evaluate aortic regurgitation. Many of these invasive techniques utilize a scale from 1 to 4+ to evaluate the severity of the aortic regurgitation. This is accomplished using angiography techniques to review the degree of regurgitate back flow through the aortic valve.
Recently, however, major advances have been made using MRI to evaluate aortic regurgitation. MRI can be used to simultaneously evaluate the severity of both aortic regurgitation and left ventricle dysfunction. Past MRI techniques utilized multiple tomographic planes which made the process time consuming and difficult to analyze. In addition, the techniques focused simply on the size of the regurgitate flow jet, which has a poor correlation to regurgitate volume. However, recently developed techniques utilize a rapid single-plane cine MRI technique which can be completed in less than 10 minutes. The new technique incorporates a new grading system which is based on the presence, size, and persistence of not only the regurgitate jet, but also the zone of proximal signal loss.
Unfortunately, invasive catheter procedures, echocardiography, and MRI are associated with several problems which may limit routine clinical utilization. Invasive catheterization, for example, is extremely expensive due to the cost of the physician, support personnel, and hospital overhead. These procedures may also be associated with considerable patient risk due to their invasive nature. Additionally, although highly accurate, these procedures are quite time-consuming to perform and usually require an overnight hospital stay. Therefore, few individuals undergo evaluation of aortic regurgitation using invasive techniques.
Non-invasive echocardiography procedures may reduce costs since they can be performed on an out-patient basis, however, they still require the cost of highly skilled personnel. Echocardiography is usually performed by a highly skilled technician and study results are usually evaluated by a specialized physician (cardiologist). Reproducibility may be of concern, however, since results may vary depending on the placement of the non-invasive transducer and the ability of the operator. In addition, the use of two-dimensional imaging may potentially underestimate or overestimate the size of physiological structures since the third dimension in space cannot be evaluated. Potential patient risk may be minimized due to the non-invasive nature of the procedure. However, the time requirements may still potentially limit utilization in some patients.
Although the development of new MRI techniques may represent an advance in the clinical assessment of aortic regurgitation, the expense of such procedures is of great concern. MRI equipment is extremely expensive, and patient access is quite limited. Importantly, although no biological after-effects have been seen from MRI, the body is exposed to low energy radiation which could be potentially hazardous. Further, the operation of an MRI requires highly skilled operators including qualified technicians and a specialized physician (radiologist). Although new methods may reduce procedure time, patient preparation time is still considered very significant.
Room for improvement exists over the known methods for determining aortic regurgitation. In particular, improvement can be achieved by providing a reliable method for determining the existence of aortic regurgitation, and a method for enabling the physician to perform a semi-quantitative analysis of the volume of aortic regurgitation, which does not require an invasive procedure. Further, the state of the known art would be improved by the existence of a method for determining and quantifying aortic regurgitation that can be performed easily by relatively low cost personnel, especially if the method could be performed on the patient without the need for expensive equipment.
It is therefore one object of the present invention to provide a method and apparatus for determining the existence of aortic valve abnormalities of the type that cause aortic regurgitation. It is also an object of the present invention to provide a method and apparatus that can enable a practitioner to determine the existence of aortic regurgitation, and to perform a semi-quantitative analysis of the relative volume of aortic regurgitation.
It is a further object of the present invention to provide a method and apparatus for determining aortic regurgitation which does not require expensive equipment or invasive procedures.
In accordance with the present invention, a method is provided for identifying the existence of aortic valve abnormalities in a patient. The method comprises the steps of providing a pressure inducing means for inducing a pressure to a body part of a patient. A data receiving means is provided, which is used for receiving a stream of pulsation signal data from the patient relating to pressure response of pulsed fluid flowing through the cardiovascular system of the patient. A data processing means processes the stream of data to create an array of pulse wave forms. Wave form characteristics are then identified that denote the presence of aortic valve abnormalities.
Preferably, the data processing means is used to create a time dependant array of pulse wave forms which is graphically displayed by a graphic display means, such as a computer monitor or a paper printout.
Also, each of the pulse wave forms of the time dependant array of pulse wave forms can include a peak. Wave form characteristics that indicate the presence of aortic valve abnormalities can be identified by comparing the heights of a series of adjacent wave form peaks. The graphic display of the time dependant array can include an envelope line that extends between the peaks of adjacent wave forms. The slope of the envelope line can be used to identify the existence of aortic valve abnormalities. If the envelope line has an undulating slope, the presence of aortic valve abnormalities is suggested.
In an alternate embodiment, the time dependent wave form data can be converted to frequency dependant wave form data through the use of a Fourier transformation. Characteristics of the frequency dependant wave form data can be identified which suggest the presence of aortic regurgitation. These characteristics are identified by first identifying a first series of harmonically occurring flow signals that correspond to a xe2x80x9cmainxe2x80x9d flow of fluid forwardly through the aortic valve, and then detecting the presence or absence of a second series of harmonically occurring xe2x80x9cregurgitationxe2x80x9d flow signals corresponding to the aortic regurgitation. The first and second series of signals each have an amplitude. By comparing the amplitude A2 of a flow signal of the second series to the amplitude A1 of a flow signal of the first series, a semi-quantitative analysis of the aortic regurgitation can be performed. Additionally, a semi-quantitative relative value for the aortic regurgitation can be obtained by comparing the density D2 of the flow signal of the second series to the density D1 of the flow signal of the first series.
In accordance with another aspect of the present invention, a device is provided for identifying the existence of aortic valve abnormalities in a patient which comprises a pressure inducing means for inducing a pressure to a body part of a patient, a data receiving means for receiving a stream of pulsation signal data from the patient relating to the pressure response of pulsed fluid flowing through the cardiovascular system of the patient. A data processing means is provided for processing the stream of data to create a time dependant array of pulse wave forms. Means are provided for aiding in the identification of wave form characteristics that denote the presence of aortic valve abnormalities.
One feature of the present invention is that it enables the user to identify characteristics that denote the presence of aortic valve abnormalities (and hence, aortic regurgitation) through the use of a non-invasive pressure inducing means. This feature has the advantage of enabling the physician to determine and diagnose a condition through the use of a procedure which is minimally invasive, and which can be performed at low cost. This feature has the further advantage of enabling testing to be conducted for aortic valve abnormalities for a wide number of people, thus making such a test affordable enough to be employed as a xe2x80x9cscreeningxe2x80x9d test.
Another feature of the present invention is that data is provided which includes a first series of signals indicative of the flow of fluid forwardly through the aortic valve, and a second series of signals indicative of aortic valve regurgitation. By comparing these two signals, a semi-quantitative analysis of the volume of aortic regurgitation can be obtained. This feature has the advantage of enabling the user to obtain some quantitative data about the extent of aortic regurgitation, which is indicative of the severity of the patient""s problems.
Another advantage of this invention is that the procedure can be performed during routine blood pressure measurement. As a result, the procedure should take no more than a few minutes or so, with an automated computer having fast Fourier transformation (FFT) and Power Spectrum Display (PSD) program. Due to the use of a non-invasive cuff sphygmomanometer, the procedure should be useable by personnel having no special training for operation. Importantly, patient risk from the procedure is almost non-existent, being no greater than the risk associated with routine blood pressure measurement.
Another advantage is that personnel training time is minimized as similar devices, using oscillometric technology, are used routinely every day in hospitals and physician offices around the world. Additionally, the cost of performing the procedure should be low compared to the other state-of-the-art technologies discussed previously. Also, the use of computer automation and analysis techniques should enable the user to achieve accurate evaluations of aortic valve irregularities.
These and other features and advantages of the present invention will become apparent to those skilled in art upon a review of the detailed description of the preferred embodiment of the present invention, which presently represents the best mode perceived by the inventors of practicing this invention.